As well known, the refrigerant present in air conditioning systems, in particular those on board of vehicles such as cars, is periodically recovered and recycled for eliminating the impurities accumulated during the operation cycle. To this purpose, the refrigerant is purged from the air conditioning system by a recovery and regeneration apparatus as described in EP1367343A1.
In these types of machines the refrigerant is subjected to a regeneration cycle in which it is depurated of the impurities in it present. Air is one of these impurities that has to be purged.
Presently, the elimination of air, in machines like EP1367343A1, is done by opening purge valves at the top of containers present in the recovery and regeneration circuit. In fact, air, like any other non-condensable gas, is accumulated in the highest parts of the containers and then the opening of purge valves makes it possible to discharge it outside. The purging step has, however, the drawback of causing unavoidably the loss of refrigerant in vapour phase, which is dragged out with air. Occasionally, the lost amount can be higher than the limit allowed by regulations.
Considering that such treatment is carried out on a very high number of air conditioning systems per day, it can be understood that this produces a high accumulation of the refrigerant in the environment, causing environmental damages. Furthermore, the cumulated discharge of refrigerant leads to not negligible economical damages due to the refrigerant cost, which is remarkably grown with a new type of refrigerant, called HFO 1234yf. The discharge in the environment of refrigerant causes also safety problems, since the refrigerant HFO 1234yf is highly inflammable, and an excessive cumulated discharge in the environment can generate an atmosphere that can explode or burn causing very serious damages to things or people.
Normally, air and other non-condensable gases are purged from the storage reservoir of the regenerated refrigerant. A first type of known purging devices provides a mechanism consisting of a manual valve, which is mounted directly to the storage container of the regenerated refrigerant of existing recovery and depuration machines, assisted by a manometer and by a temperature sensor.
After checking the pressure and temperature values of the storage container with those from tables relative to the pure gas, the valve is opened for purging air present in the refrigerant directly into the environment. The purge operation proceeds, until the pressure reaches the equilibrium vapour pressure. By purging air this way, it is apparent that the loss of refrigerant cannot be controlled, owing to the discharge of the vapour entrained with air in the gaseous phase of the storage container.
A second type of known purging devices provides a mechanism consisting of a solenoid valve mounted directly to the storage container the of the refrigerant, operated by a pressure transducer and by a temperature sensor.
Once measured the temperature, the corresponding pressure is determined using the equation of state of the pure refrigerant: if the pressure transducer detects a pressure higher than the reference pressure, the microprocessor is enabled to open the solenoid valve for purging air present in the refrigerant directly into the environment. The solenoid valve blocks automatically when the pressure reaches the equilibrium vapour pressure. A second control is carried out closing the solenoid valve when a threshold weight loss ratio of the recycled refrigerant is reached. In a third method the solenoid valve is closed after checking both the values of equilibrium vapour pressure and of weight loss ratio of the depurated refrigerant.
A third type of known purging device provides a mechanism consisting of a solenoid valve mounted directly to the storage container of the refrigerant, assisted by a pressure transducer for measuring the pressure of the storage container and by a pressure transducer connected to a bulb, filled with a pure refrigerant of the same type, in contact with the container and insulated from the outer environment. Alternatively, such device can provide positioning the bulb with the pure reference gas directly in the storage container.
The use of a pressure transducer with a bulb filled with pure gas and thermally coupled to the storage reservoir allows measuring directly the vapour pressure. This way, the device can trigger the solenoid valve after checking directly the difference between the vapour pressure of the pure gas and the pressure of the container.
The methods described above have the drawbacks of discharging amounts of vapour of the refrigerant entrained with air. If an attempt is made to reduce the loss of refrigerant, for example by stopping the discharge with a control on the loss by weight of the refrigerant, there is the opposite drawback to purge not completely the air present in the refrigerant.
Refrigerating systems also exist, for example of the type described in EP1681523, where a porous membrane is provided through which a flow is conveyed comprising the vapour phase of the refrigerant and the non-condensable gases, in such a way that the membrane blocks the passage of refrigerant, leaving only the non-condensable gases to pass.
However, this solution, can be acceptable for a refrigerating system, but cannot be used in a refrigerant regeneration system, since it would not ensure a suitable purification of the refrigerant without having waste of the same and polluting the environment.